Microelectronic devices such as semiconductor chips (microelectronic elements) typically require many input and output connections to other electronic components. The input and output connections include contacts of a semiconductor chip which are generally disposed on grid-like patterns that substantially cover a surface of the device or in elongated rows which may extend parallel to and adjacent each edge of the front surface of the device, or in the center of the front surface. Typically, the devices or chips are physically mounted on a substrate such as a printed circuit board, and the contacts of the devices must be electrically connected to electrically conductive features of the circuit board.
Semiconductor chips are commonly provided in microelectronic packages, which facilitate handling of the chip during manufacturing and during mounting of the chip on an external substrate such as a circuit board or other circuit panel. For example, many semiconductor chips are provided in packages suitable for surface mounting. A common package includes a dielectric element, commonly referred to as a “chip carrier” or “substrate” with terminals formed as plated or etched metallic structures on the dielectric. These terminals typically are connected to the contacts of the chip itself by features such as thin traces extending along the chip carrier itself and by fine leads or wires extending between the contacts of the chip and the terminals or traces.
A microelectronic package may include a single chip or may include a plurality of units, each incorporating one or more chips, stacked one on top of another along a vertical dimension. Such a stacked arrangement provides a compact package.